Film balance, fluorescence recovery after photobleaching, and micro-calorimetric measurements have shown that a temperature-dependent critical phenomenon occurs in solutions of lipid vesicles. We are postulating that this anomaly is associated with the transition of multilamellar lipid vesicles into unilamellar vesicles. Specimens are prepared for electron microscopy by plunge-freezing solutions of lipid vesicles that have been maintained at the lipid critical temperature and at 5 degrees Centigrade above and 5 degrees Centigrade below the critical temperature. The specimens are cryotransferred into the electron microscope in their frozen hydrated state and examined under low dose conditions. The specimens are then assessed for the relative concentration of unilamellar and multilamellar vesicles.